A typical syngas mixture produced, for example, by coal gasification or partial oxidation, typically contains H.sub.2, CO and C.sub.1 and heavier hydrocarbons. Previously, treatment of syngas mixtures has been directed toward separating high volatile components, such as hydrogen, from low volatile components, such as carbon monoxide. This separation was achieved using several condensation, absorption and vaporization steps. The hydrocarbons present in the syngas, primarily methane, were used as a wash liquid to effect essentially complete separation of H.sub.2 and CO. The resulting CO--C.sub.1 + hydrocarbon mixture was then separated at low pressure by conventional distillation techniques. Such processes are described in U.S. Pat. Nos. 4,102,659 and 4,338,107.
Alternatively, CO and C.sub.1 + hydrocarbons were separated from the H.sub.2 by means of one or more partial condensation steps, followed again by conventional distillation at low pressure to separate the CO--C.sub.1 + hydrocarbon mixture. One such process is described in U.S. Pat. No. 4,217,759.
U.S. Pat. No. 4,270,939 discloses a process whereby separate hydrogen, nitrogen and/or carbon monoxide, and methane product streams are recovered. Separation is obtained by effecting condensation of at least a major portion of the methane content in a dephlegmator wherein separate lower boiling components are employed as indirect heat exchange refrigerants. The methane is then recovered as a low purity product stream. H.sub.2 and N.sub.2 /CO are further separated via a conventional partial condensation step and subsequently recovered as separate pure gas streams.